Massey Ferguson 4374.08 – Engine Control Unit (ECU): Aftertreatment 1 Diesel Exhaust Fluid (DEF) Pump Motor Speed

The Engine Control Unit (ECU) or Aftertreatment Control Module (ACM) detects that the DEF pump motor is running at an abnormal speed (usually too high/fast) for the amount of DEF pressure being generated. This typically means the pump is struggling to build or maintain pressure, which is most commonly caused by the pump sucking air, a clogged DEF filter, a restriction in the DEF lines, or an internal failure of the pump itself.

• 4710
• 7724S
• 5712SL
• Interim Tier 4 (2012-2015)
• 7722
• 7722S
• 7615
• 5613
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 7616
• 7618
• 5608
• 4708
• 7619
• 7626
• 7726S
• 7624
• 4707
• 4709
• 5711SL
• 7614
• 7718S
• 5610
• 7620
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 5612
• 7622
• 7720
• Tier 4 (2015-2021)
• 5611
• 7715S
• 5609
• 7724
• 7714S
• 7719S
• 8600 series
• 8700 series

1. 1

   Check DEF quality and level using a refractometer or test strips to ensure no diesel, oil, or water contamination.

2. 2

   Inspect the DEF tank vent/breather tube for blockages that could create a vacuum and starve the pump.

3. 3

   Inspect DEF supply and pressure lines for kinks, rub-throughs, or damaged O-rings at quick-connect fittings that could allow air ingress.

4. 4

   Check the DEF main filter and suction strainer for clogs restricting flow.

5. 5

   Inspect the DEF pump electrical harness and pins for corrosion, moisture, or pushed-out terminals.

6. 6

   Perform a pressure test using a diagnostic tool to monitor pump speed vs. pressure. If speed maxes out but pressure stays low (under 50 psi) with no line leaks, the pump is internally defective.

1. 1

   Preparation

   Turn off the ignition and wait at least 5-10 minutes. The DEF system automatically runs a purge cycle after shutdown to pull fluid back into the tank. Wait for this to finish to avoid a pressurized DEF shower.

2. 2

   Disconnect Lines

   Place a clean catch pan under the pump module. Squeeze the release tabs on the DEF line quick-connects (supply and pressure lines) and pull them off the pump. Cap the lines immediately to prevent dirt ingress.

3. 3

   Disconnect Electrical

   Unplug the main electrical harness connector from the DEF pump module.

4. 4

   Remove the Pump

   Remove the mounting bolts securing the DEF pump module to its bracket on the chassis/tank and remove the unit.

5. 5

   Install New Pump

   Mount the new DEF pump and tighten the hardware.

6. 6

   Reconnect

   Reconnect the electrical harness. Reconnect the DEF lines, ensuring the quick-connects "click" securely into place.

7. 7

   Prime and Clear

   Turn the key to the ON position to allow the system to prime. Connect your diagnostic tool, clear the 004374.08 fault code, and run an SCR system pressure test/leak test to verify the new pump builds correct pressure at a normal RPM.